1. Field of the Invention
This invention resides in the materials and equipment used in performing slab gel electrophoresis, and particularly in the use of standards for facilitating the analysis of solute mixtures separated by electrophoresis.
2. Description of the Prior Art
One of the most effective, convenient, economical, and commonly used methods of analyzing biochemical mixtures in the investigations done in clinical and research laboratories is slab gel electrophoresis, a technique which allows a series of samples to be analyzed simultaneously and the results detected on a qualitative basis by direct visual observation or on a quantitative basis by instrumentation. For these reasons, slab gel electrophoresis is widely used for analyzing protein mixtures in cell lysates and other biological samples, nucleic acid mixtures in DNA sequencing operations, and any of the wide variety of analyses of this sort that are commonly performed by biologists and biochemists. The two-dimensional shape of a slab gel makes it useful in horizontal pulsed-filed electrophoretic separations, such as the CHEF® system of Bio-Rad Laboratories, Inc., Hercules, Calif., USA, and in two-dimensional electrophoretic separations, where the slab gel serves as the second dimension of the separation, following a linear first dimension separation which is typically performed by isoelectric focusing in an immobilized pH gradient (IPG) strip gel. These are only examples; other applications of slab gel electrophoresis will be readily apparent to the skilled biochemist.
Analyses of protein or other solute mixtures by slab gel electrophoresis are helped considerably by the use of standards which may consist of mixtures of proteins, nucleic acid fragments, or whatever type of species is appropriate to the analysis, each mixture having a known composition for separation in the same gel alongside the samples to be analyzed, providing a comparison by which the components of the sample can be identified. These standards can assume a variety of forms. Paper standards for example are often used in when electrophoresis is performed in vertically oriented slab gels, i.e., when the gel is oriented such that the direction of migration is vertical, and gel plug standards are often used when the slab gel is oriented such that the direction of migration is horizontal. In each case, the standard is commonly loaded onto the slab gel in a position adjacent to the samples to be analyzed. When the gel is the second dimension of a two-dimensional separation, the first-dimension gel strip is placed along one edge of the gel and the standard is placed along the same edge at one end of the gel strip.
Among the various standards that are commercially available are precast gel plugs of Bio-Rad Laboratories, Inc. A set of plugs of agarose that contain DNA size markers embedded in the agarose are available from this supplier under the product name “DNA Size Marker, H. wingei” (Catalog No. 170-3667). To use this product, the user cuts a plug to the desired dimensions with a razor blade and then inserts the cut plug into the slab gel with a flat-bladed implement referred to as a “spatula.” The use of these plugs thus involves individual handling of the plugs by the user which makes the procedure susceptible to user error and the possible loss of gel plug material. The same supplier also supplies plug kits that include plastic molds to enable one to cast one's own standard-containing agarose plugs in the laboratory. These kits are available under the product names “CHEF Mammalian Genomic DNA Plug Kit” (Catalog No. 170-3591), “CHEF Bacterial Genomic DNA Plug Kit” (Catalog No. 170-3592), and “CHEF Yeast Genomic DNA Plug Kit” (Catalog No. 170-3593). The casting of these plugs by the user adds to the tasks that the user must perform and, like the preformed plugs, requires the handling of individual pieces of gel material by the user.
Among the other standards of the prior art are those of New England Biolabs, Inc., Beverly, Mass., USA. The New England Biolabs standards consist of modified syringes filled with agarose with standards embedded in the agarose. These standards are sold under the product names “Yeast Chromosome PFG Marker” (Catalog No. NO345S), “Lambda Ladder PFG Marker” (Catalog no. NO340S), and “Low Range PFG Marker” (Catalog No. NO350S). To use these standards, the user depresses the syringe plunger to extrude the agarose containing the embedded standards, then slices off the desired amount for insertion in the gel. Similarly to the products described in the preceding paragraph, this entails the handling of a bare plug by the user.
These and other limitations of the prior art are addressed by the present invention.